The present invention relates to a method of producing a photosensitive lithographic printing plate, which requires no development processing and provides a printing plate having an excellent press life, and to a lithographic printing plate precursor used therein. More specifically, the invention relates to a method of producing a lithographic printing plate, by which the plate-making can be simply performed without development processing, the lithographic printing plate made can be directly mounted on a printing machine as it is to undergo printing operations and the plate-making can be achieved with a printing machine, and with a printing plate precursor used in such a plate-making method.
In general the lithographic printing plate has a lipophilic image area capable of accepting ink during the printing process and a hydrophilic non-image area capable of accepting a fountain solution. As a precursor of such a lithographic printing plate, the presensitized plate (i.e., the PS plate) having a lipophilic photopolymer layer on a hydrophilic support has so far been used widely. The plate-making method generally applied thereto comprises exposing the presensitized plate to light via images, such as a lith film, and then removing the non-image area by dissolving it in a developer. The desired printing plate is obtained using such a plate-making method.
In the plate-making process of the conventional presensitized plates, a step of dissolving and removing non-image areas after an exposure operation is required. Making such an additional wet processing unnecessary or simple is one of the subjects of desired improvements in the prior art. Recently in particular, the disposal of liquid wastes discharged with the progress of wet processing has become a great concern in the industrial world from the viewpoint of consideration for the global environment. Therefore, the request for improvement in this respect has become stronger and stronger.
The method as one of simple plate-making methods which comprises utilizing an image recording layer which makes it possible to remove the non-image areas of a printing plate precursor during the general printing process, and carrying out development on a printing machine after exposure, thereby obtaining the final printing plate, is proposed. The system for making a lithographic printing plate according to the aforementioned method is referred to as a xe2x80x9con-press developmentxe2x80x9d system. As a specific example thereof, mention may be made of a method in which the image recording layer soluble in a fountain solution or an ink solvent is employed and the non-image areas is removed mechanically by contact with the impression cylinder or the blanket cylinder installed in a printing machine. However, the on-press development system has a great problem that the non-image area component of the image recording layer imparts a danger of impairing printing quality, e.g., printing stain, when removed from the printing plate precursor by dissolution action or mechanical contact.
The plate-making technique which has lately drawn considerable attention as another trend in this field is a computer-to-plate technique wherein the digitized image information is carried on highly converging radiant rays, such as laser beams and the scanning exposure with these radiant rays are given to a plate precursor, thereby directly making the printing plate without exposure through a lith film. The direct plate-making technique of this type is expected to have good effects upon simplification, labor saving and speed-up of plate-making and printing procedures. In the rapid plate-making for images with gradation, however, the scanning exposure with laser beams is at a disadvantage by requiring much labor, cost and time. Therefore, it is desired to develop a plate-making method which not only enables the recording of images by an areal exposure system suitable for plate-making of gradation images but also has simplicity and rapidity equivalent to those in making printing plates by the computer-to-plate system using laser beams.
As a means to meet such a requirement, attempts to utilize the photoresponse characteristics of photocatalytic substances for plate-making have been made. For instance, JP-A-9-131914 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses the method in which the coating film of a hydrophobic substance formed on the surface of a photocatalytic substance is irradiated with active rays (or active light) to be converted into a hydrophilic substance in the irradiated area; as a result, hydrophilic areas and hydrophobic areas are distributed imagewise to make a printing plate. Similarly to the above reference, JP-A-10-35131 also discloses that the hydrophobic adsorption film formed on the surface of, e.g., silicone resin, silica or alumina undergoes polarity conversion by irradiation with active rays to form imagewise distribution of hydrophilic and hydrophobic areas, thereby making a printing plate. In addition, World Patent Application WO99/08158 also discloses the method in which the polarity conversion of photocatalytic substances by irradiation with light is utilized for lithography. These conventional arts are all inferior in sensitivity, so that a great irradiation amount of light is required for the polarity conversion and this requirement imposes a restriction upon the practical use of the foregoing conventional arts. Accordingly, it is necessary to improve the sensitivity on condition that photocatalytic substances are employed.
An object of the invention is to meet the present-day needs for reduction of environmental impacts in the field of the plate-making and answer to the market request of not only making it possible to record images by areal exposure but also to realize the simplicity on the same level as the drawing system by laser scanning has. More specifically, the object of the invention is to provide a method of making a lithographic printing plate wherein no development processing is required, the plate-making can be performed by simple operations or as the printing plate precursor is directly mounted on a printing machine, the staining on the printing plate surface is reduced and the areal exposure can be adopted for recording images, and to provide a printing plate precursor used therein.
As a result of our investigations made into various material systems capable of producing a phenomenon of polarity conversion from hydrophilicity into hydrophobicity by irradiation of light with the intention of solving the aforementioned problems, it has been found that there were combinations of materials undergoing mutual reaction by the action of photocatalysts to convert their polarity among the systems wherein compounds susceptible to reduction, such as the salts of metals having a weak ionization tendency, and compounds susceptible to oxidation, such as organic compounds having hydroxyl or carboxyl groups, are present together. By further studies based on this finding, the invention has come to be achieved.
Specifically, embodiments of the invention are as follows:
1. A method of producing a lithographic printing plate; comprising
a step of providing on a support a layer that has a hydrophobic surface and comprises an oxidizable material and a reducible material, and
a step of irradiating imagewise with active rays in the presence of a photocatalytic metal compound, wherein the oxidizable material in the irradiated area is decomposed imagewise to convert the layer surface in the irradiated area surface into hydrophilic property and form an imagewise distribution of hydrophilic areas and hydrophobic areas.
2. The method of producing a lithographic printing plate as described in the above item 1, wherein the photocatalytic metal compound is dispersed in the state of grains in the layer comprising an oxidizable material and a reducible material or provided in the form of a thin film so as to be in contact with the layer comprising an oxidizable material and a reducible material.
3. The method of producing a lithographic printing plate as described in the above item 1 or 2, wherein the reducible material is a salt of a metal element situated behind hydrogen in the order of ionization tendency.
4. A lithographic printing plate precursor, comprising a support having thereon a layer that has a hydrophobic surface and comprises an oxidizable material and a reducible material and; when the layer is irradiated imagewise to active rays in the presence of a photocatalytic metal compound, forming an imagewise distribution of hydrophilic areas and hydrophobic areas by the conversion of the irradiated area surface into hydrophilic property through the imagewise removal of the oxidizable material in the irradiated area.
5. A method of forming images, comprising imagewise irradiating a layer comprising an oxidizable material and a reducible material with active rays in the presence of a photocatalytic metal compound, and decomposing imagewise the oxidizable material in the irradiated area to convert the irradiated area surface into hydrophilic property and form imagewise distribution of hydrophilic areas and hydrophobic areas.
A primary feature of the invention is that to the making of a printing plate is applied a newly found phenomenon that, when the material system comprising an oxidizable material (i.e., a material which is oxidized), a reducible material (i.e., a material which is reduced) and grains of a photocatalytic metal compound is irradiated with active rays, the redox reaction is caused between the oxidizable material and the reducible material to result in the polarity conversion of the material system from hydrophobicity (i.e., hydrophobic property) into hydrophilicity (i.e., hydrophilic property). Moreover, the polarity conversion proceeds efficiently owing to the presence of the reducible material in this material system, so that the effective speed of light irradiation is high. Therefore, this material system can have a practical sensitivity.